The present invention relates to means for protecting high voltage overhead electrical transmission cables from wet environment corona losses.
Such cables are subject to corona losses and corona noise relating to partial electrical discharges and also decreased breakdown voltage, especially in wet environments such as during or after rainfall. Water droplets on the high voltage lines intensifies the electrical field producing corona and decreases the arc-over voltage between the lines. Thus, the distance separating three lines of a 3-phase transmission cable must be large enough to accomodate this problem during wet weather. This leads to higher costs as larger towers and additional right of ways are required.
Johansen et al. U.S. Pat. No. 3,930,113 recognizes the problem of wet weather corona losses. In the embodiment of FIG. 6 of that patent, water absorbent material such as glass fiber strands are intermingled with conductive strands and retained in place by an outer porous material, such as sintered steel. The glass fibers are stated to convey water faster in the axial direction than the radial direction for use in channelling the water along the fibers for subsequent removal, presumably at a number of water expulsion sites or spouts 5 (shown in FIG. 5). One disadvantage of this system is the requirement of such sites due to insufficient capacity in the fiber glass wicks to retain the water until the rain subsides and is permitted to evaporate away.
Another known technique for reducing corona loss is to increase the effective circumference of the power line as by contacting the conductor eccentrically with a large radius conductive material. This approach is disclosed in McLoughlin U.S. Pat. No. 3,286,020. However, there is no suggestion in that patent of any means for reducing corona problems caused by a wet environment.